The present invention relates generally to systems and methods for transmitting data. More specifically, the present invention relates to systems and methods for combining and transmitting compressed digital video data having different resolutions over communication channels.
Video services are provided by a spectrum of different video content suppliers. For example, residential digital video services may include digital television, Video On Demand (VOD), Internet video streaming, etc.—each service typically providing video data displayable at a single resolution. Common standardized resolutions for residential home video services include D1 video resolution of 720×486, HDTV with up to 1920×1080 resolution interlaced or progressive horizontal lines.
Video data is transmitted in a bitstream, or a continuous sequence of binary bits used to digitally represent compressed video, audio or data. The bitstream is transmitted over a transmission channel. One problem with existing transmission channels is their ability to transport video data for multimedia streaming applications. In these applications, the video data requires significant bandwidth from a communication channel. Since transmission of video data with existing communication channels is often excessive, compression is an approach that has been used to make digital video images more transportable. Digital video compression schemes allow digitized video frames to be represented digitally in much more efficient manner. Compression of digital video makes it practical to transmit the compressed signal using digital channels at a fraction of the bandwidth required to transmit the original signal without compression.
The video service providers typically rely on real-time encoders and pre-compressed video server storage systems to compress, and transmit the video data. These encoders and video server storage systems typically transmit data at a single resolution. In addition, both are likely to be in a remote site, away from the video service recipient.
During transmission of the compressed video data from provider to the recipient, it is common for video data to be added to the transmission by an auxiliary video content supplier. For example, local advertisers may insert local advertising video into a real time live broadcast, such as one or more local commercials in a nationally broadcast sporting event. Preferably, all digital video data provided by an auxiliary video content supplier may be combined with the compressed video data from service provider.
Auxiliary video content suppliers also use encoders that typically provide compressed video having a single resolution. When the resolution of video content provided by the auxiliary video content supplier does not match the resolution of video content provided by the initial video service provider, the resolution of one or both bitstreams may need to be changed for most digital video receivers (for example, digital cable set-top boxes, DTV and DBS receivers) to seamlessly display the transition from one content to another. Unfortunately, resolution conversion typically requires complete decoding and re-encoding. This decoding and re-encoding is computationally complex for each bitstream being decoded, and the complexity scales dramatically for a real time live broadcast, such as a nationally broadcast sporting event. In addition to being computationally demanding, decoding and re-encoding also requires specialized hardware, such as specialized ASIC encoding and decoding hardware and frame buffer memory chips.
Further, a compressed video bitstream is generally intended for real-time decoded playback. The decoded real-time playback must be done at 30 frames per second for NTSC standard video and 25 frames per second for PAL standard video. This implies that all of the information required to represent a digital picture must be delivered to the destination in time for decoding and display in a timely manner. The computational time required for complete decoding and re-encoding processes may compromise timely delivery and real-time decoded playback.
Thus, there is a need for combining compressed video data having different resolutions without introducing excessive transmission complexity.